1. Field of the Invention
The present invention relates to industrial vehicles, such as material handling vehicles, and more particularly to operating autonomously guided industrial vehicles.
2. Description of the Related Art
Industrial vehicles of various types, including lift trucks, are used to move items at a facility such as a factory, a warehouse, a freight transfer station, or a retail store. Traditionally these vehicles were controlled by an on-board human operator. As industrial vehicles became more sophisticated, a new category of autonomous guided vehicles evolved. An autonomous guided vehicle (AGV) is a form of mobile robot, that without a human operator, transports goods and materials from one place to another in a constrained environment, such as a factory or a warehouse.
Some AGV's followed a wire buried in the floor and thus were limited to traveling along a fixed path defined by that wire. Guidance technology developed further so that the vehicle did not have to be confined to a fixed path. Here reference markers, referred to as fiducials, were placed at various positions in the facility. In one implementation, each fiducial had a unique appearance or an optically readable element, e.g., a unique barcode. An AGV that needed to travel to a certain location would determine a sequence of fiducials to that location and then travel from one fiducial to the next one in that sequence. An optical sensor on the AGV sensed adjacent fiducials as the vehicle travelled and the unique appearance or code of each fiducial enabled the vehicle to determine its present location and the travel direction along the desired sequence. Even more sophisticated navigation systems have been developed that employ a video camera and image recognition software to guide the AGV along a desired path that was previously learned by the navigation system.
Regardless of the particular navigation system that was used, an AGV often had difficulty when an obstacle blocked the desired path. For example, an employee might leave a pallet of goods in an aisle being travelled by the AGV. Sensors on the AGV detected the obstacle and the controller stopped the vehicle before striking the obstacle. The AGV, however, remained stopped as long as the obstacle blocked the desired path, as the navigation system lacked the intelligence to determine another path that avoided the obstacle. The vehicle remained stationary until an employee happened to notice the event and either removed the obstacle or manually guided the vehicle around the obstacle.
Thus it is desirable to provide a mechanism for handling incidents in which the AGV is unable to continue operating along an intended path.